1. Field of the Art
The present invention relates to a controllable, motor-driven undercarriage, comprising a first frame having freely rotatable supporting wheels and a second frame having driving wheels, said frames being adapted for relative motion and being locked in various relative positions.
2. Statement of the Prior Art
The invention relates to undercarriages in general, but has found particular application in connection with wheeled chairs, drivable beds, warehouse waggons, and trucks. In the following the invention will be described in association with wheeled chairs, but it is to be understood that the undercarriage is not limited to such vehicles.
A known wheeled chair such as that disclosed in U.S. Pat. No. 3,920,093, comprises a lower rectangular frame having a freely rotatable non-driven supporting wheel at each corner. A vertical shaft extends through the center of the frame, the shaft at its lower end carrying a driving wheel and at its upper end carrying a seat on which the user may sit. At the level of the seat there is provided a horizontal tube-formed gripping ring which is carried by substantially vertical struts attached to the frame. The wheeled chair is so designed that the seat, the driving wheel and the supporting wheels can swing concurrently relative to the frame, a fact which entails that all the wheels and the seat always point in the same direction.
The known chair can be rotated 360.degree. on the spot, and theoretically it can be driven in any direction in which the seat and the wheels are pointing.
When driving the chair the user must produce a relative swinging movement between the frame and the seat in order to change the driving direction of the chair. The user must then grip the gripping ring and swing both himself and the seat until he or she adopts the position in which the wheeled chair is to be driven.
A disadvantage of such a known wheeled chair is the need for a comparatively large manual force to effect the relative swinging movement between the wheels and the frame, a fact which is especially unfavourable for users having a small physical strength. Further, such a wheeled chair will, when driven from one place to another, require that the user maintains a firm grip on the gripping ring to avoid undesired relative movements between the frame and the seat, such an undesired relative movement easily leading to unstable and wavy driving.
From U.S. Pat. No. 1,311,726 there is known a tractor which comprises four freely rotatable non-driven supporting wheels, but the function thereof is primarily to stabilize the normal direction of travel of the tractor, that is straight forward or straight backward. The tractor also comprises two driving wheels mounted on an inner annular frame which can be rotated relative to an outer frame on which the freely rotatable supporting wheels are mounted. It is possible to drive the tractor sideways, but then the inner frame must be manually rotated the desired angle whilst the tractor remains at rest, and the driving of the tractor cannot be resumed before the driving wheels have taken the position which determines the direction in which the tractor has to be driven.
U.S. Pat. No. 2,874,791 discloses a unit having driving wheels driven by individual reversible motors. However, the reversible motors are mounted on a frame which cannot be rotated relative to the main unit in which the frame is mounted. Accordingly, this known unit cannot be driven in a sideways direction.
A motor-driven wheeled vehicle is known from U.S. Pat. No. 3,404,746 in which a frame carries supporting wheels and driving wheels. However, all the supporting wheels are not freely rotatable, and only one driving wheel is mounted on the frame. It is true that a sideways driving can be accomplished with the vehicle according to this patent specification but two of the supporting wheels must then be swiveled by a winding handle and locked in a given position. When an opposite sideways driving is to be effected, the two mentioned supporting wheels must be released and the two remaining wheels swiveled and locked in a predetermined position.